Yea I agree I wouldn't buy a particular card I was chasing without its redemption, I'm sure there would be people out there that don't care about the redemption.
Here is someone selling redeemed redemptions without the actual card, so the redemptions are virtually worthless on their own...
You can get 21+ cards graded for less than $15 each, I think well worth doing for high end cards that you want to keep in your collection knowing they will stay in Pristine condition.
As to adding to their value, I think as grading NRL cards becomes more popular it may add some value to high...